The objective of this proposal is to confirm and extend recent observations that human T ("HTL") region gene products detected by aloantisera exist on PHA and Con A activated peripheral blood lymphocytes. Preliminary studies indicated that the lectin activated peripheral blood lymphocytes express additional antigenic structures that are not the classical HLA-A,B,C nor DRw antigens, but share, nevertheless, a common structure, B2 microglobulin with HLA-A,B and C alloantigens. We have shown that these antigens are in remarkable linkage disequilibrium with HLA-A locus gene products. The putative TL region determinants were also detected in a leukemic lymphoblastoid cell line, MOLT 4, by two alloantisera, K and SF48. These platelet-absorbed antisera detect non-HLA determinants unique to T lymphocytes activated by certain mitogens. K antiserum is in linkage with HLA-A1, while SF48 antiserum is in linkage with HLA-A3. By analogy to the genetics of the mouse, it was hypothesized that these antigenic structures are the counterparts of the Tla locus antigens and were, therefore, tentatively named "HTL." Our objectives are: a) to extend our original observation and look for additional "HTL" antisera. This will be done by assessing the reactivity of platelet-absorbed pregnancy sera directed against resting and lectin activated autologous lymphocytes; b) to study the tissue distribution of HTL antigens by testing all HTL sera against resting and lectin activated lymphocytes of peripheral blood lymphocytes and thymocytes. In addition, all HTL sera will be tested against T leukemic cells in the acute phase and in remission; c) to study the immunogenetics and polymorphism of this system through informative normal and recombinant families; and d) to biochemically characterize the HTL antigenic determinants recognized by the selected alloantisera.